Thursday, May 28, 2015

New paper finds 'strong' 'evidence for a direct sun–climate connection during the mid-Holocene'

A new paper published in Quaternary Science Reviews finds "strong coherence" between the Asian Monsoon/climate and solar activity proxies during the mid-Holocene from 8,800 to 6,100 years ago.

Using a stalagmite proxy with remarkable resolution of up to 2 years, the paper demonstrates "evidence for a direct sun–climate connection during the early mid-Holocene" with "strong coherence at 200-yr cycle [the de Vries solar cycle], suggesting that solar output was actively involved as a primary contributor" to climate variability and the Asian Monsoon. The authors, "speculate that these centennial-scale AM (Asian Monsoon) changes might be regulated by the positive feedbacks of oceanic/atmospheric interactions to the solar activity under the condition of the retreat of continental ice-sheets."

The author's speculated "positive feedbacks of oceanic/atmospheric interactions to the solar activity" may also represent another solar amplification mechanism by which small changes in solar activity may be amplified to large-scale effects upon climate.

Horizontal axis is thousands of years ago, top 4 graphs are proxies of the Asian Monsoon, curve in 2nd graph is summer solar isolation

d18O is a proxy of precipitation (and temperatures) and correlated to the Asian Monsoon. 14C is a proxy of solar activity. Bottom graph is a wavelet analysis showing a strong periodicity at around 200-years related to the de Vries solar cycle (indicated encircled in red in graph above at around 200 year periodicity).

Highlights

A record of 2-yr-resolution Asian Monsoon variability between 8.8 and 6.1 ka B.P.

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Persistence of centennial Asian monsoon oscillations during the early mid-Holocene.

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Evidence for a direct sun–climate connection during the early mid-Holocene.

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New insights into the interplay of the ice-sheets and the tropical ocean on the AM in the early mid-Holocene.

Abstract

Climate during the early Holocene was highly variable due to the complex interplay of external and internal forcing mechanisms. The relative importance for them on the Asian monsoon (AM) evolution yet remains to be resolved. Here we present two-to six-yr-resolution oxygen isotope (δ18O) records of five stalagmites, four of which are annually-laminated, from Qingtian Cave, central China, revealing detailed AM variability between 10.9 and 6.1 ka BP. Over the contemporaneous periods, the δ18O records agree well with each other at multi-decadal to centennial timescales. When pieced together with the previously published isotopic data from the same cave, the final δ18O record reveals detailed AM variability from the last deglaciation to the mid-Holocene, consistent with other cave records. The most striking feature of the δ18O record is the recurrence of centennial-scale oscillations, especially during the annually-counted period (8.8–6.1 ka BP). Cross-wavelet analyses between the δ18O record and solar proxies show strong coherence at 200-yr cycle, suggesting that solar output was actively involved as a primary contributor. The AM depression at 8.2 ka BP is indistinguishable in amplitude and pattern from a series of weak AM events after 8 ka BP. We speculate that these centennial-scale AM (Asian Monsoon) changes might be regulated by the positive feedbacks of oceanic/atmospheric interactions to the solar activity under the condition of the retreat of continental ice-sheets.